Marco Reus accepts Borussia Dortmund were not at their best in Saturday's 1-0 win at Hannover in the Bundesliga.
Dortmund moved 13 points clear of third-placed Bayer Leverkusen with the victory, which was sealed by Henrikh Mkhitaryan's long-range strike.
But Reus said the display was not up to scratch after a bright start.
"Quite simply, we didn't play as well as we had done in the opening 10 minutes or so," Reus told the Bundesliga's official website.
"To be brutally honest, it wasn't one of our best performances.
"We didn't play the kind of football we are capable of for long periods of both halves.
"That's why it was a scrappy encounter and that's why we only won 1-0."
Reus refused to blame a slippery pitch for Thomas Tuchel's side being out of sorts.
"That's no excuse because it was the same for the Hannover players," he said.
"Of course it is not easy to play in these conditions - it was cold and then it started raining.
"But that's not the reason we didn't play as well as we have done in recent weeks.
"In the past, we wouldn't have won a game like that.
"As it is, we have stretched our lead over third place. That was important and does us good."